The present invention relates to a solid electrolytic capacitor used in various electronic apparatuses and a method of manufacturing the capacitor.
It has recently been desired that electronic capacitors installed around CPUs in personal computers have large capacitances and small overall dimensions. In addition, it is desired that the capacitors have not only a small equivalent series resistance (ESR) but also a small equivalent series inductance (ESL) so as to provide an improved transient response at high frequencies.
FIG. 21 is a perspective view of a conventional solid electrolytic capacitor, and FIG. 22 is a cross sectional view of the capacitor. FIG. 23 is a perspective view of a capacitor element in the conventional solid electrolytic capacitor. The conventional solid electrolytic capacitor 55 includes plural capacitor elements 56.
As shown in FIG. 23, the capacitor element 56 includes a rectangular anode body having a long side L and a short side W made of either an aluminum foil having its surface area increased by etching or a baked block of valve metal powder (e.g. tantalum or niobium) with a positive electrode lead (not shown) embedded therein (not shown). The anode body includes a positive portion 58 and a negative portion 59 separated by a resist 57 in a direction along the long side L. The negative portion is immersed in electrolyte liquid for anode-oxidization (anodizing), thus being coated with a dielectric oxide layer (not shown) on its surface. Then, a solid electrolyte layer (not shown) and a negative electrode layer 60 are developed in this order on the dielectric oxide layer.
The capacitor elements 56 are joined at both short sides W to one another with a positive electrode lead terminal 61 and a negative electrode lead terminal 62, respectively. The capacitor elements 56 are then encapsulated in a resin package 63 so that a positive electrode terminal 61a and a negative electrode terminal 62a respectively provided to the positive electrode lead terminal 61 and the negative electrode lead terminal 62 are exposed to the outside of the resin package 63. Thus, the capacitor 55 includes a positive electrode terminal 61a and a negative electrode terminal 62a on respective short sides W thereof disposed opposite to each other. This arrangement allows the capacitor 55 to have a large capacitance and small overall dimensions and to be surface-mounted.
FIG. 24 illustrates measurements of the ESL of the conventional solid electrolytic capacitor. The longer the capacitor, the higher the ESL becomes. Under the condition that the length of the capacitor is unchanged, a capacitor of Ta-pellet-lead-terminal type including the capacitor elements having anode bodies made of tantalum powder connected to the lead terminal has a large ESL, and a capacitor of Al-foil-lead-terminal type having the anode bodies made of aluminum foil connected to the lead terminal has a small ESL. A capacitor of Al-foil-edge-contact type including the capacitor element having the anode body made of aluminum foil contacting at its edge has the smallest ESL.
The conventional solid electrolytic capacitor shown in FIGS. 21 to 23 includes the capacitor element 56 having the positive portion 58 and the negative portion 60 on the rectangular anode body of aluminum foil electrically connected to the positive electrode lead terminal 61 and the negative electrode lead terminal 62, respectively, provided along the short sides W of its rectangular shape. This arrangement reduces the ESR and the overall size and increases the capacitance. However, as apparent from FIG. 24, the conventional solid electrolytic capacitor fails to improve the ESL.
In a preferred embodiment, a capacitor element includes an anode body made of valve metal and having a substantially-rectangular shape. The capacitor element has positive and negative portions separated in a first direction parallel to a short side of the rectangular shape, a dielectric oxide layer over the negative electrode, a solid electrolyte layer over the dielectric oxide layer, and a negative electrode layer over the solid electrolyte layer.
A capacitor includes at least one of the capacitor elements, and preferably a plurality of the capacitor elements stacked one on another, an insulating enclosure encapsulating the capacitor elements, an external positive electrode provided on an exterior of the insulating enclosure at a first long side of the rectangular shape and extending in a second direction parallel to the long side, the external positive electrode being connected to the positive portion of the capacitor elements, and an external negative electrode provided on an exterior of the insulating enclosure at a second long side of the rectangular shape and extending in the second direction, the external negative electrode being connected to the negative electrode layer of the capacitor elements.
The solid electrolytic capacitor has reduced ESR and ESL while having a small overall size and a large capacitance.